U.S. patent number 7,935,422 [Application Number 12/782,252] was granted by the patent office on 2011-05-03 for urethane polyol precursors for coating compositions.
This patent grant is currently assigned to PPG Industries Ohio, Inc.. Invention is credited to Thomas G. Rukavina.
United States Patent |
7,935,422 |
Rukavina |
May 3, 2011 |
Urethane polyol precursors for coating compositions
Abstract
Unsymmetrical polyurethane polyol prepolymers are disclosed for
use in the formation of coating compositions. The prepolymers are
prepared as a reaction product of a diisocyanate with a short chain
aliphatic dial and a long chain polymeric diol. The prepolymers are
intended as the first component for reaction with a second
component polyisocyanate in a two-component coating composition.
The coating compositions exhibit excellent abrasion resistance and
weatherability, and are particularly useful as coatings for
polymeric window transparencies.
Inventors: |
Rukavina; Thomas G. (New
Kensington, PA) |
Assignee: |
PPG Industries Ohio, Inc.
(Cleveland, OH)
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Family
ID: |
34795439 |
Appl.
No.: |
12/782,252 |
Filed: |
May 18, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100227169 A1 |
Sep 9, 2010 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10765252 |
Jan 27, 2004 |
7732555 |
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Current U.S.
Class: |
428/423.1;
528/65; 428/425.5; 528/49; 528/45 |
Current CPC
Class: |
C08J
7/046 (20200101); B32B 27/40 (20130101); C08G
18/44 (20130101); C08G 18/664 (20130101); C08J
7/0427 (20200101); C08G 18/73 (20130101); B32B
17/1033 (20130101); C08G 18/12 (20130101); C09D
175/06 (20130101); B32B 17/10018 (20130101); C08G
18/12 (20130101); C08G 18/792 (20130101); B32B
2307/584 (20130101); B32B 2457/20 (20130101); B32B
2369/00 (20130101); Y10T 428/31551 (20150401); Y10T
428/31601 (20150401); Y10T 428/31507 (20150401); C08J
2475/00 (20130101); Y10T 428/31598 (20150401); B32B
2605/006 (20130101); B32B 2307/712 (20130101) |
Current International
Class: |
B32B
27/40 (20060101); C08G 18/64 (20060101); C08G
18/80 (20060101) |
Field of
Search: |
;428/423.1,425.6
;528/45,49,65 |
References Cited
[Referenced By]
U.S. Patent Documents
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4034017 |
July 1977 |
Chang et al. |
4403085 |
September 1983 |
Christenson et al. |
5939188 |
August 1999 |
Moncur et al. |
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Primary Examiner: Tran; Thao T.
Attorney, Agent or Firm: Siminerio; Andrew C.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a divisional of U.S. patent application Ser.
No. 10/765,262, filed on Jan. 27, 2004, which is herein
incorporated by reference in its entirety.
Claims
What is claimed is:
1. A coating composition, comprising the reaction product of: a) a
polyurethane polyol precursor comprising the reaction product of:
i) a diisocyanate; ii) an aliphatic diol having 1-6 carbon atoms;
and iii) a polymeric diol having at least one oxycarbonyl linkage
and having from 5-20 carbon atoms; b) a polyisocyanate, wherein the
coating composition comprises a molar ratio of diisocyanate:
aliphatic diol: polymeric diol from about 1:1.9:0.1 to about
1:1.1:0.9; and wherein the polyurethane polyol consists of hydroxyl
termination.
2. The coating composition as in claim 1, wherein the
polyisocyanate is selected from
2,4,6-trioxo-1,3,5-tris(6-isocyanatohexyl)hexahydro-1,3,5-triazine,
N-isocyanatohexylaminocarbonyl-N,N'-bis(isocyanatohexyl)urea, the
biuret of hexanediisocyanate, polymeric methane
diisocyanatediisosocyanate, and polymeric isophorone
diisocyanate.
3. The coating composition as in claim 1, wherein the composition
further comprises a catalyst for promoting reaction of the
polyurethane polyol precursor with the polyisocyanate.
4. The coating composition as in claim 1, wherein the catalyst is
selected from dibutyltin dilaurate, dibutyltin diacetate, stannous
octoate, butyl stannoic acid, and bismuth carboxylate.
5. The coating composition as in claim 1, wherein the composition
further comprises one or more additives selected from the group
consisting of antioxidants, colorants, UV absorbers, light
stabilizers, and surfactants.
6. The coating composition as in claim 1, wherein the diisocyanate
of the polyurethane polyol precursor is selected from
2,2,4-trimethylhexamethylene diisocyanate, 1,6-hexamethylene
diisocyanate, 1,1'-methylene-bis-(4-isocyanatocyclohexane),
4,4'-methylene-bis-(cyclohexyl diisocyanate), hydrogenated toluene
diisocyanate, 4,4'-isopropylidene-bis-(cyclohexyl isocyanate),
1,4-cyclohexyl diisocyanate, 4,4'-dicyclohexyldiisocyanate, and
3-isocyanato methyl-3,5,5-trimethylcyclohexyl diisocyanate, and
mixtures and combinations thereof.
7. The coating composition as in claim 1, wherein the aliphatic
diol is selected from 1,2-propanediol, ethyl-1,3-hexanediol,
1,6-hexanediol, 2-methyl propanediol, and 1,5-pentanediol, and
mixtures and combinations thereof.
8. The coating composition as in claim 1, wherein the polymeric
diol is selected from polycarbonate diols and polycaprolactone
diols, and mixtures thereof.
9. The coating composition of claim 1, wherein the aliphatic diol
is a linear aliphatic diol, and wherein the polymeric diol is a
linear polymeric diol.
10. A coating composition comprising the reaction product of: a) a
polyurethane polyol precursor comprising the reaction product of:
i) a diisocyanate; ii) an aliphatic diol having 1-6 carbon atoms;
and iii) a polymeric diol having at least one oxycarbonyl linkage
and having from 5-20 carbon atoms; and b) a polyisocyanate, wherein
the polyurethane polyol precursor comprises the reaction product of
2,2,4-trimethylhexamethylene diisocyanate, 1,5-pentanediol, and
polyoxohexylene carbonate diol.
11. A coating composition comprising the reaction product of: a) a
polyurethane polyol precursor comprising the reaction product of:
i) a diisocyanate; ii) an aliphatic diol having 1-6 carbon atoms;
and iii) a polymeric diol having at least one oxycarbonyl linkage
and having from 5-20 carbon atoms; and b) a polyisocyanate; wherein
the polyurethane polyol precursor comprises the reaction product of
2,2,4-trimethylhexamethylene diisocyanate, 1,5-pentanediol, and
polyoxohexylene carbonate diol; and wherein the polyurethane polyol
precursor is further reacted with
2,4,6-trioxo-1,3,5-tris(6-isocyanatohexyl)hexahydro-1,3,5-triazine
in the presence of dibutyltin dilaurate as a catalyst.
12. A substrate having a coating on at least one surface thereof,
said coating comprising the reaction product of: a) a polyurethane
polyol precursor comprising the reaction product of: i) a
diisocyanate; ii) an aliphatic diol having 1-6 carbon atoms; and
iii) a polymeric diol having at least one oxycarbonyl linkage and
having from 5-20 carbon atoms; b) a polyisocyanate, wherein the
coating composition comprises a molar ratio of
diisocyanate:aliphatic diol:polymeric dial from about 1:1.9:0.1 to
about 1:1.1:0.9; and wherein the polyurethane polyol consists of
hydroxyl termination.
13. A substrate as in claim 12, wherein the substrate is glass.
14. A substrate as in claim 12, wherein the substrate comprises a
polymeric material.
15. A substrate as in claim 14, wherein the substrate comprises a
polycarbonate sheet.
16. The substrate of claim 12, wherein the aliphatic diol is a
linear aliphatic diol, and wherein the polymeric diol is a linear
polymeric diol.
Description
FIELD OF THE INVENTION
The present invention relates to coating compositions exhibiting
excellent abrasion resistance and weatherability, and more
particularly to precursors for use in preparing such coating
compositions.
BACKGROUND OF THE INVENTION
Safety glass is a term commonly used to describe a glass-plastic
laminate designed to reduce the severity of lacerative injuries
resulting upon impact sufficient to break the glass. A plastic film
is laminated to a glass sheet so that upon impact sufficient to
break the glass, the film adheres to the glass fragments,
minimizing their dispersion. To be useful as safety glass, a
laminate must have high energy absorption to minimize concussive
injuries upon impact, high tensile and tear strength to prevent
rupture of the film by glass fragments, sufficient adhesion between
the layers to reduce lacerative injuries by minimizing the
dispersion of glass fragments, and high optical quality. Moreover,
the safety glass laminate must retain these properties over a wide
range of temperature and humidity conditions.
Commercially employed safety glass, particularly in automobile
windshields, is commonly a multiple laminate of two plies of glass
with an interlayer of polymeric material, such as plasticized
polyvinyl butyral. An alternative to this trilayer type of safety
glass laminate is a bilayer laminate having a single ply of glass
with a plastic layer. Upon impact sufficient to break the glass in
a bilayer windshield, the danger from glass fragments inside the
passenger compartment is greatly reduced because there is no
interior glass ply. However, since the inner layer is not protected
by an interior glass ply, the plastic film must have good
weathering properties, chemical stability, and abrasion resistance,
to provide durability for the requisite safety and optical
quality.
To fulfill such requirements of safety glass, a number of different
compositions have been proposed for use a protective coatings. For
example, U.S. Pat. No. 3,931,113 discloses polyester urethanes for
use in safety glass windshields, which are formed from a one-step
bulk polymerization involving the reaction of cycloaliphatic
diisocyanate with a low-molecular weight diol, such as butanediol,
and with a poly(butylene adipate) or poly(butylene azelate)
polyester component or a hydroxy-terminated polycaprolactone
polyester. U.S. Pat. No. 4,923,757 discloses an abrasion and
solvent resistant protective coating in the form of a polyurethane
film which is made through a two-component system, with a first
component of an aliphatic isocyanate-terminated prepolymer reacted
with a second component of a linear polyol, such as a polyester or
a polyether diol. The first prepolymer component is prepared by
reacting a symmetrical triol with an isocyanate.
Such traditional coating compositions have demonstrated their
usefulness as coatings for certain substrates, such as glass.
However, carbonate diols, such as polyester diols are expensive,
which increases the costs of the coated product. Also, when used on
polymeric substrates, such coating compositions typically require a
very high solids content to achieve an effective coating. Coating
compositions with higher solids content, however, typically have a
higher viscosity, and therefore often require solvents for flow
coating processes. Such solvents can have an adverse effect on
polymeric substrates during coating thereof. Moreover, certain
moieties within the coating composition are believed to be more
readily subject to oxidation, such as ethers, esters and
carbonates, and therefore have reduced weatherability when used as
protective coatings.
Accordingly, while prior art coating compositions have proven
useful, there is a need for improved coating compositions that are
simple and cost-effective to manufacture, and which increase the
durability and weatherability of the coating.
SUMMARY OF THE INVENTION
The present invention is directed to prepolymers used in the
formation of coating compositions, as well as coating compositions
manufactured from such prepolymers and products coated with such
compositions. The prepolymers represent unsymmetrical polyurethane
polyols, and in particular trimeric or highly oligomeric polyols
prepared as a reaction product of a diisocyanate with a short chain
aliphatic diol and a long chain polymeric diol. The prepolymers are
intended as the first component for reaction with a second
component polyisocyanate in a two-component coating
composition.
The prepolymer is an unsymmetrical polyurethane polyol in the form
of a low viscosity, non-crystalline substantially 100 percent
solids material. The polyurethane polyol is represented by the
reaction product of a diisocyanate, an aliphatic diol having 1-6
carbon atoms, and a polymeric diol having at least one oxycarbonyl
linkage and having from 5-20 carbon atoms. Desirably, the aliphatic
diol is a short chain diol having an odd number of carbon atoms.
The polymeric diol is desirably a polycarbonate diol or a
polycaprolactone diol. Desirably, the ratio of the
diisocyanate:aliphatic diol:polymeric diol is from about 1:1.9:0.1
to about 1:1.1:0.9.
In a further embodiment, the present invention is directed to a
coating composition comprising the reaction product of such a
polyurethane polyol precursor and a polyisocyanate, desirably in
the presence of a catalyst. Such a coating composition is
particularly useful in combination with a substrate such as glass
or, more desirably, a polymeric sheet, to form a cured layer
thereon.
In yet a further embodiment, the present invention is directed to a
substrate coated with such a coating. Examples of useful substrates
include glass and polymeric materials such as a polycarbonate
sheet.
The term "solids" embraces all non-volatile constituents of the
compositions, i.e., binders, pigments, fillers, additives, etc.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
As used herein, spatial or directional terms, such as "inner",
"outer", "left", "right", "up", "down", "horizontal", "vertical",
and the like, relate to the invention as it is described herein.
However, it is to be understood that the invention can assume
various alternative orientations and, accordingly, such terms are
not to be considered as limiting. Further, all numbers expressing
dimensions, physical characteristics, and so forth, used in the
specification and claims are to be understood as being modified in
all instances by the term "about". Accordingly, unless indicated to
the contrary, the numerical values set forth in the following
specification and claims can vary depending upon the desired
properties sought to be obtained by the present invention. At the
very least, and not as an attempt to limit the application of the
doctrine of equivalents to the scope of the claims, each numerical
parameter should at least be construed in light of the number of
reported significant digits and by applying ordinary rounding
techniques. Moreover, all ranges disclosed herein are to be
understood to encompass any and all subranges subsumed therein. For
example, a stated range of "1 to 10" should be considered to
include any and all subranges between (and inclusive of) the
minimum value of 1 and the maximum value of 10; that is, all
subranges beginning with a minimum value of 1 or more and ending
with a maximum value of 10 or less, and all subranges in between,
e.g. 1 to 6.3, or 5.5 to 10, or 2.7 to 6.1.
The present invention is directed generally to an unsymmetrical
polyurethane polyol. Polyurethane polyols are particularly useful
as prepolymers or precursors for producing polyurethane coating
compositions. The polyurethane polyols of the present invention are
considered unsymmetrical urethane polyol trimers, in that they
include a short chain moiety having hydroxy functionality and a
long chain moiety having hydroxy functionality, both of which are
linked together through urethane linkages derived from an
isocyanate. The polyurethane polyols of the present invention are
prepared by reacting a diisocyanate with a short chain diol and a
long chain polymeric diol, thereby producing an unsymmetrical
urethane polyol trimer through the reaction of the short chain diol
with one end of the diisocyanate and the reaction of the long chain
polymeric diol with the other end of the diisocyanate.
The diisocyanate, which is employed to make the polyurethane polyol
prepolymer as a precursor, is a cycloaliphatic compound and
preferably a Binuclear compound bridged by an isopropylidene group
or an alkylene group of 1 to 3 carbon atoms. Among the examples of
useful diisocyanates include, but are not limited to,
2,2,4-trimethylhexamethylene diisocyanate (TMDI), 1,6-hexamethylene
diisocyanate (HDI), 1,1'-methylene-bis-(4-isocyanatocyclohexane),
4,4'-methylene-bis-(cyclohexyl diisocyanate), hydrogenated toluene
diisocyanate, 4,4'-isopropylidene-bis-(cyclohexyl isocyanate),
1,4-cyclohexyl diisocyanate (CHDI), 4,4'-dicyclohexylmethane
diisocyanate (Desmodur W), and 3-isocyanato
methyl-3,5,5-trimethylcyclohexyl diisocyanate (IPDI). Mixtures and
combinations of these compounds can be employed. Particularly
desirable examples of useful mixtures of diisocyanates include TMDI
and Desmodur W, commercially available from Degussa and Bayer.
As noted, the diisocyanate is reacted with a short chain diol and a
long chain polymeric dial. The short chain diol is a linear
aliphatic diol, desirably having from about 1-6 carbon atoms.
Non-limiting examples of useful short chain diols include
1,2-propanediol, ethyl-1,3-hexanediol, 1,6-hexanediol, 2-methyl
propanediol, and 1,5-pentanediol, as well as mixtures and
combinations thereof. Particularly desirable are those short chain
diols having an odd number of carbon atoms, such as 1,2-propanediol
and 1,5-pentanediol. While not wishing to be bound by any
particular theory, it is currently believed by the present inventor
that reacting the diisocyanate with a short chain diol having an
odd number of carbon atoms reduces the crystallinity of the
thus-formed urethane diol, which lowers the viscosity of the
urethane diol. The short chain diol desirably has a molecular
weight of 76 to 104.
The long chain polymeric dial reacted with the diisocyanate along
with the short chain diol to form the polyurethane polyol
prepolymer may be selected from any of the chemical classes of
polymeric polyols used or proposed to be used in polyurethane
formulations. Polymeric polyols including hydroxy terminal groups
with at least one oxycarbonyl linkage, and desirably including from
5-20 carbon atoms are preferred, and in particular those having
molecular weights in the range of 200-6000. Particularly desirable
polymeric diols include polyesters, polyesteramides,
polycarbonates, and polycaprolactones. Particularly useful are
aliphatic polycarbonate diols, and desirably those having a
molecular weight of 500 to 2000, more preferably 500 to 1000. Such
polycarbonate diols can be based on alkyleneglycols, ether glycols
and alicyclic glycols or a mixture thereof. Polyoxohexylene
carbonate diol, 1000 molecular weight, is particularly useful, such
as KM10-1733 polycarbonate diol, available from Stahl. Non-limiting
examples of other suitable polycarbonate polyols that are
commercially available include KM10-1122, KM10-1667 (all products
of Stahl) and DESMOPHEN 2020E (product of Bayer).
Also useful as the long chain polymeric diol are polyesters
obtained by the polymerization of lactones, for example
caprolactone, such as a polycaprolactone diol, and desirably those
having a molecular weight of from 500 to 2000, more preferably 500
to 1000. Non-limiting examples of suitable polycaprolactone diols
that are commercially available include Tone 0201, 0210, 0230 and
0241 (products of Dow Chemical Co.).
The diisocyanate and the short chain aliphatic and long chain
polymeric dials are reacted in such as way so as to result in a
hydroxyl-terminated polyurethane polyol prepolymer. The prepolymers
are unsymmetrical trimeric species, prepared from 2 moles of
OH-terminated moieties and 1 mole of diisocyanate. This is
accomplished through conventional reaction schemes, by reacting a
stoichiometric excess of the diols with the diisocyanate under
substantially anhydrous conditions at a temperature between
30.degree. C. and 130.degree. C. until the reaction between the
isocyanate groups and the hydroxyl groups is substantially
complete. The diisocyanate and the diol components are suitably
reacted in such proportions that the ratio of number of isocyanate
groups to the number of hydroxyl groups is in the range of 1:1.1 to
1:6, for example within the range of 1:1.5 to 1:3. The equivalent
ratio of the diisocyanate to the short chain aliphatic dial and to
the long chain polymeric diol is desirably from 1:1.9:0.1 to
1:1.1:0.9. Accordingly, the trimeric prepolymer polyol according to
the present invention is represented by a general structure as
follows: x moles short chain diol--1 mole diisocyanate--y moles of
polyol where x+y=2.
The ratio and proportions of the short chain diol and the polyol
greatly effect the viscosity of the thus formed prepolymer. The
viscosity of such prepolymers can be particularly important,
particularly when they are intended for use with coating
compositions, and particularly those for flow coating processes.
The solids content of such prepolymers, however, is also important,
in that higher solids content is typically preferred to achieve
desired properties from the coating, such as weatherability,
scratch resistance, etc. In conventional coatings, coating
compositions with higher solids content typically require greater
amounts of solvent material to dilute the coating in order to
reduce the viscosity for appropriate flow coating processes. The
use of such solvents, however, can adversely effect the substrate
surface, particularly when the substrate surface is a polymeric
material. It has been discovered through the present invention that
the viscosity of the prepolymer can be appropriately tailored to
provide a material with lower viscosity levels at higher solids
content, thereby providing an effective coating without the need
for excessive amounts of solvents which can deleteriously effect
the substrate surface.
Moreover, symmetrical polymers typically have higher viscosity as
well. Thus, the more asymmetry that is designed into the prepolymer
the lower will be the viscosity. Accordingly, providing a trimer
polyurethane prepolymer with specific ratios of the short chain
diol and the polyol with respect to the diisocyanate produces an
effective prepolymer composition particularly useful for
polyurethane coating compositions. The viscosity of the prepolymer
can be appropriately tailored, i.e. decreasing the viscosity by
increasing the amount of the short chain diol and by decreasing the
amount of the polyol, within the ratios set forth above. When less
polyol is used the product becomes cheaper and weatherability is
improved. However, a greater proportion of the short-chain dial can
cause an increase in the weight percent urethane content, and an
increase in the urethane content can lead to an increase the
viscosity. Accordingly, there is a limit as to how much short chain
diol can be added to achieve the desired properties. It has been
discovered that the prepolymers prepared in accordance with the
present invention within the content ratios set forth herein can
achieve an effective tradeoff between performance and
viscosity.
As indicated, the polyurethane polyol prepolymers are particularly
useful as a first component in two-component coating composition.
In such a use, the second component is a polyisocyanate capable of
reacting with terminal hydroxyl groups on the polyurethane polyol
prepolymer in a polymerization reaction to form a polyurethane
coating composition. The polyisocyanate for such polymerization
reaction can be any suitable isocyanate, and in one nonlimiting
embodiment is a triisocyanate. Non-limiting examples of useful
materials include aromatic triisocyanates such as
tris(4-iso-cyanatophenyl)methane (Desmodur R),
1,3,5-tris(3-isocyanato-4-methylphenyl)-2,3,6-trioxohexahydro-1,3,5
triazine (Desmodur IL); adducts of aromatic diisocyanates such as
the adduct of 2,4-tolylene diisocyanate (TDI,
2,4-diisocyanatotoluene) and trimethylolpropane (Desmodur L); and
especially from aliphatic triisocyanates such as
N-isocyanatohexylaminocarbonyl-N,N'-bis(isocyanatohexyl)urea
(Desmodur N),
2,4,6-trioxo-1,3,5-tris(6-isocyanatohexyl)hexahydro-1,3,5-triazine
(Desmodur N3390), and
2,4,6-trioxo-1,3,5-tris(5-isocyanato-1,3,3-trimethylcyclo-hexylmethyl)hex-
ahydro-1,3,5-triazine (Desmodur Z4370). Also useful are the biuret
of hexanediisocyanate, polymeric methane diisosocyanate, and
polymeric isophorone diisocyanate.
The coating compositions may be prepared by dissolving the
polyurethane polyol prepolymer in a suitable solvent and reacting
with the polyisocyanate, desirably in the presence of a tin
catalyst, under anhydrous conditions at a temperature between
30.degree. C. and 130.degree. C. until the reaction between the
isocyanate groups and the hydroxyl groups is substantially
complete. The polyurethane polyol prepolymer and the polyisocyanate
components are suitably reacted in such proportions that the ratio
of number of isocyanate groups to the number of hydroxyl groups is
in the range of 1.3:1.0 to 0.9:1.0.
Reaction between the polyurethane polyol prepolymer and the
polyisocyanate can be facilitated through a suitable catalyst. Tin
catalysts are desirable in this regard, with dibutyl tin dilaurate
being one example of a particularly suitable catalyst. Examples of
other catalysts include, but are not limited to, dibutyltin
diacetate, stannous octoate, butyl stannoic acid, and bismuth
carboxylate. Other additives can also be included in the reaction
to impart specific properties as is known in the art. For example,
one or more additives such as antioxidants, colorants, UV
absorbers, light stabilizers such as hindered amine light
stabilizers, and surfactants can be included in the coating
composition. Non-limiting examples of useful antioxidants include
IRGANOX 1076, commercially available from Ciba Geigy. Non-limiting
examples of useful UV absorbers include TINUVIN 130, commercially
available Ciba Geigy, and SANDOVAR 3206, commercially available
from Clarion. Non-limiting examples of useful hindered amine light
stabilizers include SANDOVAR 3056, also commercially available from
Clarion. Non-limiting examples of useful surfactants include BYK
306, commercially available from BYK Chemie.
The coating compositions of the present invention can be used to
coat a substrate surface, and the present invention is further
directed to substrates including such a coating thereon. Suitable
substrates for use with the coating compositions can include glass
and polymeric substrates. As the coating compositions prepared with
the polyurethane polyol prepolymers exhibit a low viscosity with a
high solids content, they are particularly suitable for use as
coatings on polymeric substrates, where conventional high solids
content coatings are typically higher in viscosity and therefore
require volatile solvents for coating procedures, which can degrade
the polymeric substrate.
Transparent materials such as transparent copolymers and blends of
transparent polymers are particularly suitable as substrates for
optical articles to which the coating composition of the present
invention can be applied. In one non-limiting embodiment of the
invention, the substrate is an optically clear polymerized organic
material prepared from a thermoplastic polycarbonate resin, such as
the carbonate-linked resin derived from bisphenol A and phosgene,
which is sold under the trademark LEXAN (product of GE Plastics,
General Electric Co.); a polyester, such as the material sold under
the trademark MYLAR (product of E. I. du Pont de Nemours & Co.,
Inc.); a poly(methyl methacrylate), such as the material sold under
the trademark PLEXIGLAS (product of Rohm and Haas Co.);
polymerizates of a polyol(allyl carbonate) monomer, especially
diethylene glycol bis(allyl carbonate), which monomer is sold under
the trademark CR-39 (product of PPG Industries, Inc.), and
polymerizates of copolymers of a polyol (allyl carbonate), e.g.,
diethylene glycol bis(allyl carbonate), with other copolymerizable
monomeric materials, such as copolymers with vinyl acetate, and
copolymers with a polyurethane having terminal diacrylate
functionality, as described in U.S. Pat. Nos. 4,360,653 and
4,994,208; and copolymers with aliphatic urethanes, the terminal
portion of which contain allyl or acrylyl functional groups, as
described in U.S. Pat. No. 5,200,483; poly(vinyl acetate),
polyvinylbutyral, polyurethane, polymers of members of the group
consisting of diethylene glycol dimethacrylate monomers,
diisopropenyl benzene monomers, and ethoxylated trimethylol propane
triacrylate monomers; cellulose acetate, cellulose propionate,
cellulose butyrate, cellulose acetate butyrate, polystyrene and
copolymers of styrene with methyl methacrylate, vinyl acetate and
acrylonitrile.
Desirably, the polymeric substrate material including the coating
composition applied thereto can be in the form of optical elements
such as windows, piano and vision correcting ophthalmic lenses,
exterior viewing surfaces of liquid crystal displays, cathode ray
tubes, e.g. video display tubes for televisions and computers,
clear polymeric films, automotive transparencies, e.g.,
windshields, aircraft transparencies, plastic sheeting, etc.
For example, in one non-limiting embodiment, an automobile window
can be prepared from a thermoplastic polycarbonate resin, such as
that sold under the trademark LEXAN, with the coating composition
of the present invention applied as a weather layer on the outboard
side of the window to increase the weatherability of the window.
Alternatively, an automobile window can be prepared as a
glass/LEXAN laminate, with the glass as the outboard layer and the
coating composition of the present invention applied as a layer on
the inboard side of the laminate.
The coating composition of the present invention can be applied to
the substrate surface using any known coating procedures. In one
non-limiting embodiment, the coating composition is flow coated
over the substrate surface by an automated flow-coating system in
which the surface tension of the liquid pulls a coherent sheet of
liquid across the substrate surface as the mechanical flow-coating
device traverses across the substrate sheet. An automatic
flow-coating device typically consists of an articulating arm that
holds a nozzle connected to a pressure pot where the resin solution
is held. The arm runs on a track above the sheet to be coated. The
rate of flow of the liquid is adjusted using the pressure pot. The
rate of traverse of the articulating arm is set using a
potentiometer. The nozzle distance from the sheet is optimized and
kept constant, via the articulating arm. This is particularly
important for curved sheets. The thickness of the coating is
determined by the initial viscosity of the resin solution and the
rate of solvent evaporation. The evaporation rate is mainly
controlled by the solvent choice and the cubic feet/minute airflow
in the ventilated coating booth. Alternatively, the coating
compositions can be prepared and cast in an appropriate mold to
form a desired structure, which can then be applied as a layer to a
suitable substrate, such as through a lamination process, or may
used as a monolithic structure.
The present invention will be further understood from descriptions
of specific examples that follow.
EXAMPLES
Example 1
Example 1 demonstrates the viscosity measurements of trimeric
unsymmetrical polyurethane polyol prepolymers made in accordance
with the present invention. In particular, as shown in Table 1, two
(2) separate trimeric unsymmetrical polyurethane polyol prepolymer
samples were prepared in accordance with the present invention. In
particular, Samples 1 and 2 include varying equivalent ratios of
polymeric polyol and aliphatic short chain diol with respect to
diisocyanate.
TABLE-US-00001 TABLE 1 Equivalent Viscosity (cps) Weight
95%/90%/85% Sample Component (g/eq.) Equivalents Weight Weight %
Solids 1 1733.sup.2 436.5 0.2 87.3 33.47 3400/2000/900 1,2 38 1.8
68.4 26.22 propanediol TMDI.sup.1 104.14 1.0 105.14 40.31 2
1733.sup.2 436.5 0.3 130.95 43.55 4600/3000/1600 1,2 38 1.7 64.6
21.48 propanediol TMDI.sup.1 104.14 1.0 105.14 34.97
.sup.12,2,4-trimethylhexamethylene diisocyanate .sup.2KM10-1733,
available from Stahl
Each of Samples 1 and 2 prepared as such were dissolved in
diacetone alcohol solvent at 95% solids, 90% solids and 85% solids,
and the viscosity of the thus prepared solutions were each
measured.
As shown in Table 1, the viscosity of the prepolymer in solution
can be decreased by increasing the amount of aliphatic short chain
diol and decreasing the amount of polymeric polyol. For example,
when the equivalents of the polymeric polyol is decreased from 0.3
to 0.2 in the above noted Samples, the viscosity at 95% solids in
diacetone alcohol solvent drops from 4600 to 3400 centipoises
(cps).
Example 2
Four separate coating compositions were prepared including the
following materials and proportions:
TABLE-US-00002 WEIGHT % POLY- POLY- POLY- POLY- COMPONENT MER A MER
B MER C MER D Cyclohexanone 19.22 19.23 19.32 19.20 Solvent
PREPOLYMER TMDI.sup.1 13.95 14.94 14.11 15.04 Polycarbonate
diol.sup.2 23.17 18.62 23.44 18.73 1,5-pentanediol 11.04 12.58 3.72
4.21 1,2-propanediol -- -- 2.72 3.08 1,6-hexanediol -- -- 4.22 4.8
Polyisocyanate.sup.3 28.73 30.78 29.10 30.97 Dibutyltin dilaurate
0.38 0.38 0.37 0.38 catalyst ADDITIVES UV Absorbers 1.92 1.92 1.93
1.92 Hindered Amine 0.77 0.77 0.77 0.77 Light Stabilizers
Antioxidants 0.39 0.39 0.39 0.39 Surfactants 0.39 0.39 0.77 0.39
.sup.12,2,4-trimethylhexamethylene diisocyanate .sup.2KM10-1733,
available from Stahl
.sup.32,4,6-trioxo-1,3,5-tris(6-isocyanatohexyl)hexahydro-1,3,5-triazine
(Desmodur N3390)
Polyurethane polyol prepolymers were first prepared by combining
the prepolymer components including the TMDI, polycarbonate diol
and the short-chain diol components, and heating them in an oven at
93.3.degree. C. for 24 hours. The reaction mixture was then cooled
to 80.degree. C. Each of the polyurethane polyol prepolymers formed
were clear, with a slight yellow tint.
Each of the polyurethane polyol prepolymers were then combined with
the cyclohexanone solvent, the catalyst, and the additives and
maintained at 80.degree. C. for 1 hour. After 1 hour, the contents
were cooled to room temperature, and were clear. The polyisocyanate
was then added, and the mixture was placed in a cool water bath.
After about 30 minutes, the mixture again became clear.
2,4-pentanedione was then added to the mixture to stop the
reaction. Each of the thus-formed polymers was degassed in a large
polypropylene beaker.
Each of the polymers A-D formed as such were flow coated onto 4
inch by 4 inch polycarbonate sheets, and allowed to dry until
tack-free. Each of the polymers A-D were separately flow coated
onto 12 inch by 12 inch polycarbonate sheets, and cured in an oven
at 120.degree. C. for 3 hours.
After curing, a set of the sheets coated with each of the polymers
A-D were abrasion tested using a standard Taber abrasion test with
CS10F wheels (one pair for all samples), 500 grams each wheel. The
wheels were re-surfaced before each cycle (25 cycles). Test
conditions were conducted at a temperature of between
21.degree.-24.degree. C. and 50-60% relative humidity. Average
scattered light haze for a given number of Taber cycles was
determined, with the results shown below.
Unexposed Samples
TABLE-US-00003 % Haze at number of Cycles Coated with Sample 0 100
300 500 1000 Polymer A 0.7 1.6 2.6 3.7 6.2 Polymer B 0.5 1.3 2.6
3.6 5.9 Polymer C 0.4 1.1 2.3 3.3 6.0 Polymer D 1.1 1.8 2.6 4.4
8.4
Separately, sets of the sheets coated with each of the polymers A-D
were Taber tested for abrasion resistance after long term exposure,
under a standard QUV-B exposure test procedure over a period of
1000 hours, representing the equivalent of about three years of
outdoor exposure. The results are shown below.
Exposed Samples--1000 hours QUV-B Exposure--3 yr. Equivalent
Outdoor
TABLE-US-00004 % Haze at number of Cycles Coated with Sample 0 100
300 500 1000 Polymer A 0.3 0.7 1.1 1.7 2.7 Polymer B 0.3 1.2 2.4
3.6 7.1 Polymer C 0.3 0.6 1.5 2.3 4.7 Polymer D 1.3 1.4 3.4 5.3
12.7
The results of these tests demonstrate that the use of the trimer
polyurethane prepolymer in the coatings of the present invention
provide abrasion resistance over time, without significant haze,
particularly when considered in view of known compositions
incorporating only a carbonate polyol as in the polyurethane
compositions. Moreover, with Sample A, the haze that develops for
Sample A after 1000 cycles and after considerable weathering
exposure is close to 2%, the minimum acceptable specified by ANSI
for automotive glazing safety.
It will be readily appreciated by those skilled in the art that
modifications may be made to the invention without departing from
the concepts disclosed in the foregoing description. Moreover, as
will be appreciated by one of ordinary skill in the art, the
preferred operating parameters described above can be adjusted, if
required, for different substrate materials and/or thicknesses.
Accordingly, the particular embodiments described in detail herein
are illustrative only and are not limiting to the scope of the
invention, which is to be given the full breadth of the appended
claims and any and all equivalents thereof.
* * * * *